Multiple deploy/undeploy leaks memory in PCRegistry
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Key: OPENJPA-285
URL: https://issues.apache.org/jira/browse/OPENJPA-285
Project: OpenJPA
Issue Type: Bug
Components: kernel
Environment: Geronimo
Reporter: Pinaki Poddar
Kevin Miller reported:
Geronimo is running out of PermGen space in some simple deploy/ undeploy
scenarios involving OpenJPA. The cause of the problem seems to be the _metas
table in PCRegistry. _metas is a ConcurrentReferenceHashMap with WEAK reference
keys and HARD reference values. The keys are the PersistenceCapable classes.
While the values are the metadata for these classes which are maintained by the
internal Meta class.
The cause of the ClassLoader memory leak is simple -- if any of the
objects/classes held by the Meta class (e.g. fieldTypes) have also been loaded
by the same ClassLoader used to load the PersistenceCapable class, the
PersistenceCapable class (the weak key) will never be GCed. The value of the
HashMap entry will always maintain a hard reference to the ClassLoader. Since
the ClassLoader will never be GC'ed, the the the pcClass Class object will
never be GC'able...
The problem can be easily recreated using current Geronimo trunk and the
Geronimo Daytrader application.
Patrick Linskey suggested:
Change PCRegistry.fieldTypes to be String[] instead of Class[], and
dematerialize them as needed.
Robert Burrell Donkin/Marc Prud'hommeaux both pointed out that alternatives
such as to
listen for the death of a ClassLoader and manually unregistering metadata would
be more costly in terms of complexity.
This patch follows Patrick's suggestion.
1. Changes the Meta.fieldTypes to String[] from Class[]
2. Adapts the enhanced bytecode accordingly to the modified method signatures
3. PCRegistry getFieldTypes() load the fields' declared type using the same
loader that loaded the owner pc class.
Note: For a class C and its field f, CL(c) == CL(f) is not always true. (Kevin
Miller)
But CL(c) will be able to load declared type of f either directly or
via one of its parent (Craig Russel)
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